Defense Secretary James Mattis has expressed opposing views to US President Donald Trump about global warming, calling climate change a clear and present threat to national security.

“Climate change is impacting stability in areas of the world where our troops are operating today,” Mattis said in a written testimony provided to the Senate Armed Services Committee as stated by media on Tuesday.

According to his congressional testimony quoted in ProPublica, Mattis said he believed that global warming and climate change were posing a clear and present threat to US national security.

“It is appropriate for the [US military] Combatant Commands to incorporate drivers of instability that impact the security environment in their areas [affected by global warming such as the new water routes opening in the thawing Arctic] into their planning,” he warned.

The Pentagon chief’s concerns go in stark contrast with the beliefs of President Trump who does not think climate change is a big problem worth any attention.

“I don’t think [climate change] in any major fashion exists … So I am not a believer, and I will, unless somebody can prove something to me, I believe there’s weather. I believe there’s change, and I believe it goes up and it goes down, and it goes up again... but I am not a believer [in global warming], and we have much bigger problems," he said in one interview.

On other occasions, Trump has not only denied climate change, but also referred to it as a plot targeting the US economy.

The president has argued that global warming was “created by and for the Chinese” to attack American industries.